One life zone common to all biomes is the riparian lifezone. Riparian ecosystems are adjacent to rivers and lakes. Because they have a proximate water table, the flora and fauna that reside there are often very different from the organisms beyond the riparian zone. I used to research a tree species in riparian zones. Here is a biography of Russian olive (Elaeagnus angustifolia) to get a sense of what happens in this life zone. Although the specific characteristics of a riparian zone in the tundra and in the grassland (two of your favorite ecosystems to write about, students) might not be exactly the same, the dynamics of moving water give rise to similar adaptations in the species that reside there.
Russian olive (E. angustifolia) is an invasive, nitrogen-fixing, non-native tree that colonizes riparian and fallow agricultural areas. Russian olive has several characteristics that facilitate its survival in the arid conditions of terraced riparian zones. The seeds have long dormancy and can accumulate in the soil and germination when water becomes available. Birds consume the seeds and travel through the riparian zone thereby dispersing the seeds. Russian olive also spreads vegetatively by rhizomes. It is nearly impossible to remove via cutting because of this feature. Since Russian olive actively reproduces through both sexual (seeds) and asexual (vegetative spread) means, it can both perpetuate genetic diversity and exploit the survival benefits of clonal reproduction.
In riparian areas, Russian olive outcompetes native willow and cottonwood species because the regime of frequent over-bank flooding in historic mesic environments of riparian areas no longer exists. Native cottonwood seeds require overbank flooding that recedes slowly over several weeks. Most riparian forests are now disconnected from the nearby hydrology because the stream channel is narrowed by man-made structural components (dams, bank stabilization) that control the flow and prevent overbank flooding from occurring.
Russian olive was originally planted by the Army Corps of Engineers to stabilize stream banks in the mid-20th century. The extensive root networks of Russian olive rhizomes reinforce bank stability and therefore perpetuate the permanence of riparian soils and banks. This is good for the Russian olive and bad for the native plants described above.
Birds and small mammals consume the Russian olive seeds and travel through the riparian zone thereby dispersing the seeds.
Gaddis, M., & Sher, A. (2012). Russian olive (Elaeagnus angustifolia) removal in the western United States: multi-site findings and considerations for future research. Sustainability, 4(12), 3346-3361.
Online Teaching Tip
This is a grading comment in my online biology course. I write lecture essays or post lecture videos, or confirm mathematical understanding while giving constructive grading feedback. That’s right- I am lecturing more at the end of the module than at the beginning. This is student-directed learning. They explore. They raise topics they are interested in. I make sure we are meeting the learning outcome. I present my expert cognitive perspective at the end of the module, as a review before the summative assessment.